The title organic–inorganic hybrid salt, (C₇H₁₁N₂)₂[V(C₂O₄)₂O(H₂O)]·2H₂O, shows a distorted octahedral coordination environment for the vanadium(IV) atom in the anion (point group symmetry 2), with four O atoms from two symmetry-related chelating oxalate dianions and two O atoms intransconfiguration from a coordinating water molecule and a terminal vanadyl O atom. In the crystal, (001) layers of cations and anions alternate along [001]. The anionic layers are built up by intermolecular O—H...O hydrogen bonds involving the coordinating and solvent water molecules. The cationic layers are linked to the anionic layersviaN—H...O hydrogen bonds between the pyridinium group and the non-coordinating O atoms of the oxalate group. The 4-(dimethylamino)pyridinium cations are also engaged in π–π stacking with their antiparallel neighbours [centroid-to-centroid distance = 3.686 (2) Å]. Considering all supramolecular features, a three-dimensional network structure is accomplished.

As part of our studies on the synthesis and the characterization of oxalate-bridged compoundsM–ox–M(ox = oxalate dianion andM= transition metal ion), we report the crystal structure of a new oxalate-bridged Mn^IIphase, {(CH₆N₃)[Mn(C₂O₄)Cl(H₂O)]·H₂O}_n. In the compound, a succession of Mn^IIions (situated on inversion centers) adopting a distorted octahedral coordination and bridged by oxalate ligands forms parallel zigzag chains running along thecaxis. These chains are interconnected through O—H...O hydrogen-bonding interactions to form anionic layers parallel to (010). Individual layers are held togetherviastrong hydrogen bonds involving the guanidinium cations (N—H...O and N—H...Cl) and the disordered non-coordinating water molecule (O—H...O and O—H...Cl), as well as by guanidinium π–π stacking. The structural data were confirmed by IR and UV–Visible spectroscopic analysis.

Based on the potential redox and catalytic ability of oxovanadium complexes, our goal was to characterize the physical properties of two such complexes to be used as mediators for laccase. Computational studies, TD-DFT calculations and docking simulations were performed to elucidate the interaction between laccase and the two anionic complexes (aquabis(oxalato)oxidovanadate(IV) (1) and bis(oxalato)dioxidovanadate(V)) (2), respectively. Electrochemical measurements carried out on anion complexes of 1 and 2 docked into laccase were compared to laccase alone, showing changes in oxidation-reduction potential and current value, especially with the oxovanadium anion of 2. Since both internal tiny magnetic fields of ferromagnetic catalysts and external applied magnetic fields were found in previous investigations to constitute effective ways to improve the oxygen transfer rate, the magnetic susceptibility was measured. A valence change proneness was confirmed with higher valence for the oxovanadium anion of 2, which is in accordance with the electrochemical results.